Project Summary Production of nanomaterials has increased continuously because of their unique physicochemical characteristics and extensive applications. There are great concerns for the potential health effects of exposure to these nanoparticles. Because of nanomaterials' small sizes and large surface areas, many studies have shown that the biological effects of nanomaterials are greater than bulk material of the same chemical composition. In 2005, the NIOSH recommended exposure limits of 1.5 mg/m3 for fine TiO2 and 0.1 mg/m3 for ultrafine TiO2, as time-weighted average concentrations (TWA) for up to 10 hr/day during a 40-hr work week. However, there are no suitable personal samplers capable of assessing the exposure level of ultrafine or nanoparticles. The overall objective of this study is to develop a personal sampler capable of collecting the ultrafine particles (nanoparticles) in the occupational environment. This sampler consists of a cyclone for respirable particle classification, a polycarbonate track-etched (PCTE) membrane filter with an acceleration nozzle to achieve nanoparticle classification, and a backup filter to collect nanoparticles. By applying high and localized filtration velocity in the nozzle, diffusion deposition of nanoparticles can be avoided in the classifying PCTE filter, and nanoparticles can be collected in the downstream backup filter. This research will lead to the development of a unique personal sampling device capable of classifying the nanoparticle fraction (d 100 nm) from the aerosol stream and collecting this fraction for gravimetric, chemical, and other analyses. This device can be used to accurately assess personal exposure to nanoparticles in terms of mass concentration and physicochemical characteristics.